1. Field of the Invention
This invention relates to methods for producing natural hydrocarbons, particularly, clean natural gas. In particular, this invention relates to methods for removing hydrogen sulfide from natural gas.
2. State of the Art
Naturally produced hydrocarbon gases typically contain a mixture of gaseous hydrocarbons and often some hydrogen sulfide. Hydrogen sulfide is toxic and has an intense, unpleasant stench. Consequently, government environmental regulations permit only small concentrations (&lt;4 ppmv) of hydrogen sulfide in commercially distributed natural gas. Moreover, hydrogen sulfide is also extremely corrosive and, if not removed, may corrode the steel pipes used to transport hydrogen sulfide-containing fluids. In severe environments, sulfide stress cracking may occur, possibly resulting in the contents of the pipe escaping into the environment. Therefore, operators of producing wells will normally separate the hydrocarbon portion of the gas from the hydrogen sulfide at the well site.
Various methods exist for removing hydrogen sulfide from gases and liquids during petroleum processing. Many of these methods involve contacting the hydrogen sulfide containing gas with an aqueous solution of organic base to neutralize the hydrogen sulfide and remove it. These schemes require regeneration plants for the organic base used, and while possibly suitable for large plants, these schemes are prohibitively expensive for smaller operations, such as at well sites or on natural gas producing off shore oil platforms. Smaller installations involve a steep capital cost, have high operating costs, and generate contaminated waste products needing subsequent disposal. Moreover, in some small operations, for example off shore oil platforms, room to build plants is at a premium. In off shore oil platforms as well as other sites, the total cost of building and operating conventional hydrogen sulfide removal plants, including the cost of transporting the required solvents to the offshore platform and waste products from the offshore platform, is prohibitive.
It would be desirable to provide a similar economical method for the selective removal of hydrogen sulfide from natural gas at the site of production.